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Accepted papers to appear in an upcoming issue

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Absorption enhancement by a period array ofnano-grooves in gold substrate

Yinghao Cao, Siwen Zhang, Xiaodong Sun, and Feng wu

DOI: 10.1364/JOSAA.393882 Received 27 Mar 2020; Accepted 29 May 2020; Posted 29 May 2020  View: PDF

Abstract: Comprehensive investigations of absorption enhancement by a period array ofnano-grooves in gold substrate are provided. A simple Fabry-Perot model is presented toexplore impact factors on absorption enhancement. The impacts of structural parameters onabsorption enhancement for an array of nano-grooves are explored and discussed. Ourcalculations show that complete absorption (about 1) can be obtained with groove depthfulfilling Fabry-Perot resonance condition. The effect of groove width on absorption for atrapezoidal groove array is slightly different with that for a rectangular groove array, becauseof the impact of single-pass loss in the grooves. Surface plasmon resonance that can carrymost of energy away from grooves and propagate along the metal surface could lead toextremely low absorption for a period array of nano-grooves. Our discussions identify twokey roles in absorption enhancement for a nano-groove array: the fundamental groove moderesonance and the generation of surface plasma polaritons. Besides, the analysis of absorptionenhancement for an array of trapezoidal grooves can also provide a comprehensivecontribution of Fabry-Perot resonance and electromagnetic interaction along the bevel edgesof the trapezoidal grooves.

Infrared and visible image fusion via joint convolutional sparse representation

Minghui Wu, Ma Yong, fan fan, Xiaoguang Mei, and Jun Huang

DOI: 10.1364/JOSAA.388447 Received 17 Jan 2020; Accepted 26 May 2020; Posted 27 May 2020  View: PDF

Abstract: Recently, convolutional sparse representation (CSR) based image fusion improves the preservation of details of source images in fusion result. This is mainly because the convolutional sparse representation has a global representation character relative to traditional sparse representation, which can improve spatial consistency in image representation process. However, during image fusion processing, it expresses infrared and visible images separately, ignoring the connections and differences between them. Further, CSR based image fusion is not able to retain both strong intensity and clear details in fusion result. In this paper, a novel fusion method is proposed, which named joint convolutional sparse representation (JCSR) based imagefusion. Specifically, we establish a joint form based on a convolutional sparse representation with local processing. This joint form is able to guarantee spatial consistency during the image representation while it can obtain distinct features (such as visible scene details and infrared target intensity). Experimental results illustrate that our fusion framework outperforms traditional sparse representation based fusion frameworks.

On Special Relativistic Effects via Classical Physics

Robert Woodruff

DOI: 10.1364/JOSAA.385646 Received 11 Dec 2019; Accepted 19 May 2020; Posted 20 May 2020  View: PDF

Abstract: We present an analytic study of light propagation in a simple Michelson-Morley interferometer as observed by inertialobservers with the desire to understand any connections among classical physics, optical physics, and special relativity. Tothat end we develop coordinate transformations of wave propagation as observed in inertial frames, i.e., non-acceleratingreference frames. We find that relativistic and other effects appear naturally as a result of finite light speed. Such effectsinclude wavefront tilt relative to the normal of energy flow with the wavefront normal tilting relative to the Poynting vector.

Characterising the Spatio-Temporal Envelope ofthe Human Visual System through the Visibilityof Temporal Aliasing Artefacts

Alex Mackin and David Bull

DOI: 10.1364/JOSAA.387475 Received 03 Feb 2020; Accepted 16 May 2020; Posted 18 May 2020  View: PDF

Abstract: Previous studies have demonstrated that the onset of temporal aliasing artefacts occurswhen the spatial displacement between samples reaches a critical distance, and that subsequentlya linear relationship exists between stimulus speed and critical sampling rates. In this paper wecarry out further experimentation using a novel experimental setup, in which a strobe light is usedto emulate impulsive temporal sampling, in order to investigate the spatio-temporal envelopeof the human visual system and the effect of stimulus. For non-periodic stimuli, experimentalresults show that critical sampling rates increase with motion speed, they decrease with stimuluswidth. These interactions can be described using simple log-linear models, and characterisedusing the Temporal Aliasing Visibility Function (TAVF) - where maximum critical frame ratesup to 1500 Hz are predicted. For periodic stimuli we demonstrate that both perceptible temporalaliasing artefacts and stimulus aliasing can cause stroboscopic effects.

A compact high-precision periodic-error-free heterodyne interferometer

Ki-Nam Joo, Erin Clark, Yanqi Zhang, Jonathan Ellis, and Felipe Guzman

DOI: 10.1364/JOSAA.396298 Received 29 Apr 2020; Accepted 16 May 2020; Posted 18 May 2020  View: PDF

Abstract: We present the design, bench-top setup, and experimental results of a compact heterodyne interferometer that achieves picometer-level displacement sensitivities in air over frequencies above 100 mHz. The optical configuration with spatially separated beams prevents frequency and polarization mixing, and therefore eliminates periodic errors. The interferometer is designed to maximize common-mode optical laser beam paths to obtain high rejection of environmental disturbances, such as temperature fluctuations and acoustics. The results of our experiments demonstrate the short- and long-term stabilities of the system during stationary and dynamic measurements. In addition, we provide measurements that compare our interferometer prototype with a commercial system, verifying our higher sensitivity of 3 pm, higher thermal stability by a factor of two, and periodic-error-free performance.

Zonal-based high performance control in adaptiveoptics systems with application to astronomy andsatellite tracking

Léonard Prengère, Caroline Kulcsar, and Henri-François Raynaud

DOI: 10.1364/JOSAA.391484 Received 26 Feb 2020; Accepted 14 May 2020; Posted 15 May 2020  View: PDF

Abstract: This paper presents a model-based approach to adaptive optics (AO) control based on a zonal (i.e. pixellised) representation of the incoming atmospheric turbulence. Describing the turbulence on a zonal basisenables to encapsulate into a control-oriented model the standard frozen-flow assumption. A multi-layerzonal model is proposed for single-conjugate AO (SCAO) systems. It includes an edge compensationmechanism involving a limited support, which results in a sparser model structure. To further reducecomputational complexity, new resultant zonal models localized in the telescope pupil are proposed,with AR1 or AR2 structures, which match the spatial and temporal cross-correlations of the incomingturbulence. Global performance of the resulting Linear Quadratic Gaussian (LQG) regulator is evaluatedusing end-to-end simulations, and is compared with several existing controllers, for two different configurations: Very Large Telescope SCAO and low earth orbit satellite tracking. Results show the highpotential of the new approach and highlight possible trade-offs between performance and complexity.

One-step fluorescence photoacoustictomography with the optical radiative transfermodel

prabodh pandey, Bharadwaj Jampu, Naren Naik, and Hari Om Aggrawal

DOI: 10.1364/JOSAA.389476 Received 29 Jan 2020; Accepted 13 May 2020; Posted 13 May 2020  View: PDF

Abstract: We present adjoint-based Jacobian as well as gradient evaluations,and corresponding reconstruction schemes to solve the fully nonlinear, opticalradiative transfer modeled one-step fluorescence photoacoustic tomographic(FPAT) problem which aims to reconstruct the map of absorption coefficientof the exogenous fluorophore from boundary photoacoustic data. Radiativetransport equation (RTE) and frequency-domain photoacoustic equation (PAE)have been employed to model light and photoacoustic wave propagation respectively. Levenberg-Marquardt and BFGS reconstruction schemes have been usedcorresponding to the evaluated Jacobians and gradients respectively. Numericalreconstructions obtained from the two schemes have been validated for scatteringdominant as well as non-scattering-dominant media in two-dimensions. To thebest of our knowledge, these are the first one-step FPAT reconstruction results inliterature based upon the optical RTE model.

Calibration methods for camera with tilted lens and three-dimensional laserscanner in Scheimpflug condition

Mingwei Shao

DOI: 10.1364/JOSAA.391906 Received 09 Mar 2020; Accepted 12 May 2020; Posted 12 May 2020  View: PDF

Abstract: A three-dimensional laser scanner has been designed and widely utilized in many fields. Lensplane is tilted according to Scheimpflug condition and optical axis is not perpendicular to the chargecoupled device plane. In this case, depth of view can be extended significantly. In this paper,analytical models for the camera with tilted lens and the laser scanner meeting the Scheimpflugcondition are presented. Based on these models, calibration procedure is detailed. We propose asimply calibration method to determine intrinsic parameters of a Scheimpflug camera. Meanwhile,two calibration methods for a laser scanner in Scheimpflug condition are detailed. According to theobtained intrinsic parameters, the laser scanner can be calibrated directly. Moreover, a simplycalibration for a three dimensional laser scanner without the help of a precise positioning system isdescribed. Experimental results show the effectiveness and high measurement accuracy of ourcalibration methods.

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